Method and apparatus for robust information coding
A digital signal is imperceptibly embedded into an input source signal, such as an image or video signal, to produce an encoded (sometimes termed "watermarked") signal. The principle of quasi-rotational symmetry is employed to facilitate detection of the embedded signal notwithstanding rotation of the encoded signal. Single or multiple degrees of symmetry can be employed. In another aspect, the digital signal is transformed to a frequency domain and phase-only filtered prior to its combination with the input source signal. In an illustrative embodiment, this filtering operation helps hide the digital signal within the source signal, and facilitates detection of the embedded digital signal even after the encoded signal has undergone various forms of corruption.
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1. In a method of steganographically processing an image signal to embed multi-bit information therein, an improvement comprising representing said information in the form of a plurality of partially overlapping quasi-rotationally symmetric patterns, and processing the image signal to imperceptibly enabled said plurality of partially overlapping quasi-rotationally symmetric patterns therein, wherein said quasi-rotational symmetry of the patterns facilitates detection of the multi-bit information from a resulting processed image signal if said processed image signal is corrupted by scaling or rotation operations.
2. The method of claim 1 in which each of said quasi-rotationally symmetric patterns encodes a single bit of information.
3. The method of claim 1 in which said plurality of quasi-rotationally symmetric patterns comprises at least four patterns, and centers of said plurality of patterns lie on a circle, thereby forming a rosette of patterns.
4. The method of claim 3 which includes processing the image signal to encode a plurality of said rosettes therein, wherein the rosettes are spaced across a representation of the image signal in a pixel domain so that a pattern of one rosette overlaps a pattern of another rosette.
5. The method of claim 4 in which patterns of one rosette overlap patterns of six other rosettes.
6. The method of claim 3 which includes providing at least one pattern in said rosette with a distinguishing feature to aid in distinguishing it from other pattern in said rosette during decoding.
7. The method of claim 1 which includes pre-processing the plurality of patterns prior to encoding the image signal therewith, said pre-processing including performing a fourier transform on said plurality of patterns to produce transformed data, and applying a filtering function to said transformed data.
8. The method of claim 7 in which the filtering function is rotationally symmetric within a spatial frequency domain.
9. The method of claim 7 in which the filtering function is phase-only.
10. The method of claim 1, further comprising storing the processed image signal on a physical medium.
11. The method of claim 10, wherein the physical medium comprises paper.
12. The method of claim 10, wherein the physical medium comprises a magnetic or electronic storage medium.
13. The method of claim 1 in which said patterns are wave patterns.
14. The method of claim 1 in which said quasi-rotationally symmetric patterns exhibit symmetry about more than one axis.
15. The method of claim 1 in which said quasi-rotationally symmetric patterns exhibit symmetry about more than two axes.
16. The method of claim 1 in which said image signal is represented as pixel data in a spatial image domain.
17. The method of claim 16 in which said processing includes adding a bit-mapped representation of said patterns to said pixel data.
18. The method of claim 1 in which the patterns exhibit said quasi-rotational symmetry when represented as pixel data in a spatial image domain.
19. The method of claim 1 in which the quasi-rotational symmetry of the patterns facilitates detection of the multi-bit information from the processed image signal if the processed image signal is corrupted by a rotation operation.
20. The method of claim 1 in which the quasi-rotational symmetry of the patterns facilitates detection of the multi-bit information from the processed image signal if the processed image signal is corrupted by a scaling operation.
21. The method of claim 1 in which the quasi-rotational symmetry of the patterns facilitates detection of the multi-bit information from the processed image signal by enabling re-registration of a corrupted, processed image signal by reference to said patterns.
22. A computer storage medium having instructions stored therein for causing a computer to perform the method of claim 1.
23. In a computer-implemented method of producing a steganographically encoded signal, the method including storing a representation of an input signal in a memory, and combining a multi-bit data signal with said input signal, the method being practiced using a programmed processor in conjunction with said memory, an improvement comprising:
- transforming the multi-bit data signal to produce a transformed signal in a complementary frequency domain;
- applying a phase-only filtering function to the transformed signal to produce a filtered signal; and
- combining the filtered signal with the representation of the input signal to effect steganographic encoding thereof, wherein the multi-bit data signal is hidden within the first signal without commercially impairing the value thereof.
24. The method of claim 23 in which the input signal is a set of image data represented as pixel data in a spatial image domain, and in which the multi-bit data signal comprises data corresponding to a plurality of quasi-rotationally symmetric patterns.
25. The method of claim 23 in which the combining step comprises adding the filtered signal to the representation of the input signal.
26. The method of claim 23 which includes representing the filtered signal as a group of pixels prior to combining same with the representation of the input signal.
27. A computer storage medium having instructions stored therein for causing said computer to perform the method of claim 23.
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Filed: May 8, 1995
Date of Patent: May 5, 1998
Assignee: Digimarc Corporation (Portland, OR)
Inventor: Geoffrey B. Rhoads (West Linn, OR)
Primary Examiner: Leo Boudreau
Assistant Examiner: Brian P. Werner
Law Firm: Klarquist Sparkman Campbell Leigh & Whinston
Application Number: 8/436,102
International Classification: G06T 900;